In this instructable I will show you how to easily make an electronic metronome, at the heart of which is a 555 timer. I found the original plans for this and the circuit diagram here.
Here is a video of the metronome.
It has two LEDs and a speaker. For each beat, it clicks and switches the LED that is lit up. You control the speed of the beats with a dial.
Step 1: Parts and Tools
9v battery snap-on connector
2 (two) 22 uF capacitors
3 (three) 1K ohm resistors
Perforated PC board
2 (two) 3V LEDs
8 Ohm Speaker (see notes below)
250K Ohm Potentiometer (see notes below)
And finally... a project box.
A project box can be just about anything that the parts will fit into, will sufficiently protect what you've built, and have some way of providing access to the controls. I used a see-through plastic box that held thumbtacks. It conveniently opens and closes for repairs and battery changes, makes it look cool, and you can easily drill holes for the controls to go through. You could buy a project box from Radioshack or find one in your house.
About the speaker: I found mine in a bad set of walky-talkies. To find out the resistance, just take a multimeter and measure the resistance across the leads or it should say on the package if you bought it. It needs to be 8 ohms!
About the potentiometer: If you click on the link, it won't take you to a 250K ohm potentiometer. That's because Radioshack doesn't have one. Instead, I found a stereo 100K pot at Radioshack and the two signal paths in sequence so it became a 200K pot (which is close enough). The diagram for this is in the next step.
Drill (if you want/need to drill holes in your project box for the controls/leds/speaker)
Glue/adhesive to hold stuff in place in the project box (I used a hot glue gun, it's easy to use and holds things well)
Breadboard (if you want to make a prototype, which you should)
Step 2: Prototype
Basically, just follow the picture below to put the circuit into your breadboard and wire it up! You can add in the switch at the +9v input or at the ground output. I used ground. Make sure to get the polarities on the capacitors and on the LEDs right! If it doesn't work, double check your connections and then make sure that the LEDs and the pot and all of the parts work. If you turn it on and it doesn't work, turn it off and make sure that no parts are hot. If any are, you may have fried them with a short or by putting them in backwards. If you are using the stereo pot, check out the wiring diagram for that below.
Step 3: Solder!
Make sure to use as little solder as possible. I didn't and I had to start over. Luckily I wasn't very far and I had more PC board. Also remember that when you flip over the PC board the pins on the IC are flipped over too, and that you should make the wires to your components longer than you need them just in case you have a problem with the project box.
When your done, test it! If it doesn't work, check your connections, check the battery, check polarities. If everything's right, you may have damaged something during soldering by overheating it.
Make sure to cut your PC board down to size. A sharp hobby knife works well. You can either cut your PC board to the smallest you can get it, or to the perfect size for your box. I cut it to the smallest I can get it and it works fine.
Below is a scan of the diagram I drew on graph paper, and the picture of the circuit diagram. Sorry my drawing is so messy, you don't have to use it, you can make your own layout. (Warning: I checked it, but I haven't thoroughly checked my drawing...so you may want to double check the circuit!)
Step 4: Assemble the Project
Next, get all of the right sized drill bits for each component, and drill your holes. Don't press too hard on the drill! I broke my case twice because I pressed down too hard when drilling.
Put everything in it's hole and screw into place the pot and switch. The pot probably has a little protrusion that you'll need to drill a little hole for right next to the big hole. This is to keep it from twisting around when you turn the knob.
And finally, hot glue your speaker and LED's!
Congratulations! You just made your own metronome! Now go show it off to people. But don't show it off in an airport.